1. Field of the Invention
The invention relates to the production of aromatic polyamides and polyamidimides which are thermoplastically processible and have high temperature stability and good mechanical properties.
2. Discussion of the Background
Aromatic polyamides with the recurring unit: EQU --CO--Ph--CO--NH--Ph--NH-- (I)
and aromatic polyamidimides with the recurring unit: ##STR1## not only have outstandingly high temperature stability and good mechanical properties, but they are also thermoplastically processible. See Elias and Vohwinkel, "Neue polymere Werkstoffe fuer die industrielle Anwendung", 2nd Series, Carl Hanser Verlag, pp. 242 ff. (1983).
Known methods of producing aromatic polyamides include the following.
1. Low temperature "solution polycondensation" by reacting aromatic dicarboxylic acid dichlorides with aromatic diamines in polar solvents (U.S. Pat. Nos. 3,287,324; 3,541,056; 3,600,350; 3,819,587; 3,767,756; 3,869,429; 3,673,143; 3,817,941 and 3,063,966; and German AS No. 22 19 703). PA1 2. Interfacial polycondensation by reaction between an aromatic dicarboxylic acid dichloride and an aromatic diamine, at the interface between an organic and an aqueous phase (German OS Nos. 19 08 297 and 23 25 139; and German Pat. No. 3,006,899). PA1 (A) at least one aromatic polycarboxylic acid selected from the group consisting of PA1 wherein R is an alkyl group with 1-4 C atoms; PA1 wherewith the said bisamide may be replaced to the extent of up to 50 mol % by a bisamide of formula EQU R--CO--NH--Ph--(Z--Ar).sub.m --Ph--NH--CO--R, PA1 (i) the viscosity number J, which is a measure of the molecular weight, is greatly increased; PA1 (ii) the color quality of the polymers is greatly improved; PA1 (iii) the polycondensation time is greatly reduced; and PA1 (iv) the molecular weight of the resulting polyamides is between 10,000 and 200,000, preferably between 20,000 and 70,000. PA1 Isophthalic acid, which may permissibly be replaced by terephthalic acid to the extent of up to 60 mol %; PA1 Trimellitic acid; PA1 The monoanhydride of trimellitic acid produced readily by heating the acid; PA1 m=0 or 1, PA1 R is an alkyl group with 1-4 C atoms, and PA1 Z is any of --O--, --S--, --SO.sub.2 --, --CO--, or --CH.sub.2 --. PA1 I. The reactants and catalysts are melted together, and pre-condensation is carried out at temperatures between 200.degree. and 380.degree. C. Then the temperature is raised to 350.degree.-390.degree. C., and the prepolymer is further condensed. The development of high molecular weights is determined by a sharp increase in the viscosity of the melt. PA1 II. A mixture of the reactants and catalysts, in powder form, is processed in a kneader, with a gradual increase in temperature from 220.degree. to 350.degree. C., until the water produced in the condensation is removed. Alternatively, it is possible to carry out the polycondensation in an extruder, again with the apparatus being charged with a mixture of the components in powder form. In the use of an extruder, the temperature is adjusted to achieve complete removal of the water of reaction. PA1 III. It is also possible to use Embodiment I to produce the precondensate from the starting material, at a temperature of 200.degree.-280.degree. C., and then to further condense the pre-condensate in a kneader or an extruder. The temperature required in an extruder is typically 280.degree.-370.degree. C., preferably 290.degree.-350.degree. C. This embodiment is particularly preferred.
Aromatic polyamides can also be produced by reaction of aromatic dicarboxylic acids with aromatic diisocyanates (German OS No. 19 28 435) or by reaction of aromatic dicarboxylic acid diaryl esters with aromatic diamines.
Thus, Brode et al describes the preparation of 4,4'-[sulfonylbis(p-phenyleneoxy)-] dianiline from p-aminophenol and 4,4'-dichlorodiphenylsulfone, and condensation of this product with aromatic acyl chlorides (e.g., terephthalic acid chloride) to aromatic polyamides with glass transition temperatures (Tg) between 230.degree. and 320.degree. C. See Polym. Prep. Am. Chem. Soc. Div. Pol. Chem., 15:761 (1974); and Adv. Chem. Ser., 142 (1975). See also Chem. Abstr. 84, 5530s, and 83, 193186f.
These methods have the disadvantage that they depend on the use of activated monomers which are difficult to handle.
Methods are also known wherein aromatic polyamides are obtained directly by reaction of aromatic dicarboxylic acids and aromatic diamines in the presence of aromatic phosphites. Solvents which have proven useful for this method are N-methyl acid amides, particularly N-methylpyrrolidone. If other dipolar aprotic solvents, such as dimethylsulfoxide, are used, no polymeric amides are obtained. See Higashi, F., et al., J. PolYm. Sci., Polym. Chem. Ed., 18:1711 ff (1980).
A method is also known wherein aromatic polyamides are produced by polycondensation in the melt, of certain dicarboxylic acids with certain diamines, in the presence of phosphorous-containing compounds (See German Patent Application P No. 36 09 011.5).
In addition to the methods mentioned above in which the condensation is carried out in a solvent, there have also been additional attempts to produce polyamides and polyamidimides in the melt. Thus, U.S. Pat. No. 3,109,836 describes a method of producing polyamides with the recurring unit (CO--Ar--NH), in which acetamidobenzoic acid is heated to 200.degree.-300.degree. C. for 3 hr., in a vacuum. This method does not result in thermoplastically processible products (in contrast to the methods according to the present invention), because the melting points of the reaction products are in the range of the decomposition temperatures or above.
A similar method is described in German OS No. 21 18 388. The reaction occurs in the solid phase. Therefore, the reaction rate is very low. It is not possible to thermoplastically process the product, for example in an extruder.
It has also been proposed to produce aromatic polyamides by transamidation of acylated aromatic amines, in the melt. In order to improve processibility of the product, mixtures of the starting products with aliphatic substances are used, instead of the pure aromatic starting compounds. The diamines are not completely acylated; only partially. Acetic acid, acetic anhydride, dimethylacetamide, or some other agent for improving flowability, is added to the reaction melt. See Keske et al., Polym. Prep., 25, Part XXV, 25 (1984); and U.S. Pat. No. 3,654,227.
U.S. Pat. Nos. 4,358,561; 4,348,513 and 4,447,574 describe production of polyamidimides by reacting acylated aromatic diamines with aromatic tricarboxylic acid anhydrides and dicarboxylic acids. If only partially acylated diamines are used as described, water-containing acetic acid is liberated during the polycondensation. The corrosive action of this acid necessitates costly special apparatus. The products have very high softening temperatures, which are in the range of the decomposition temperatures. The products are therefore unsuited for being thermoplastically processed.
The preparation of a polyimide molding powder is described in German OS 21 18 388. The dianhydride of an aromatic tetracarboxylic acid is reacted with a bisamide, or else self-condensation of an aromatic compound which has both an acetamido group and an anhydride group is carried out. Also, U.S. Pat. No. 3,654,227 describes reaction of aromatic bisamides with aromatic tetracarboxylic acid dianhydrides, to form oligomeric polyimides. In both cases, one does not obtain any high molecular weight polyamides which are thermoplastically processible.